The present invention generally relates to tools used in subterranean wells and, in a preferred embodiment thereof, more particularly provides a linear indexing tool in which pressurized fluid in the interior of the tool is automatically diverted to an exterior pressure actuatable device in response the completion of a predetermined number of indexing cycles of the tool.
Due to their very nature, subterranean wells are typically axially elongated, with their axial lengths being orders of magnitude greater than their diameters. Where such tools are remotely positioned in subterranean wells, only a limited number of actions may be taken at the earth's surface to control operation of the tools such as setting a packer within a wellbore. One of these actions is to create a controllably increased fluid pressure within the interior of the tubing string with which a particular tool is in operative fluid communication. Thus, for example, to use internal tubing pressure to hydraulically set a packer externally supported on the tubing string it is necessary to force pressurized fluid downwardly through the tubing string and then operatively apply the created fluid pressure to the particular mechanism which is used to set the packer.
Before the packer is set, however, it is desirable to apply an internal test pressure to the tubing string to verify the absence of leaks therein and/or use the internal tubing pressure to operate other pressure actuatable devices carried by the tubing string. The problem is, of course, that in conventional designs creation of this elevated fluid pressure within the tubing string sets the packer. If a tubing string leak is subsequently discovered, the completion cannot be pulled up due to the setting of the packer.
A design goal when hydraulically set packers (or other external pressure actuatable devices) are utilized has thus been to be able to create a full test pressure within the tubing string without actuating the packer or other external device, and then utilize internal tubing pressure to actuate the packer or other external device subsequent to a successful tubing pressure test.
One previously proposed solution to this problem has been to provide within the tubing string an explosive charge which, when set off, opens a port that permits pressurized fluid within the tubing string to be discharged therefrom and bypassed to the inlet of a packer setting structure. During pressure testing of the tubing string the port is blocked by a shiftable member within the interior of the string. After a successful tubing pressure test, a predetermined pressure pulse sequence is created in the tubing and detected by an electronic transducer therein. Upon detecting the predetermined pressure pulse sequence the transducer transmits an electrical output signal that detonates the charge. The resulting detonation force is used to forcible move the shiftable member to unblock the port and thereby permit internal tubing pressure to flow out of the tubing string and set the packer.
This previously proposed solution carries with it several problems, limitations and disadvantages. For example, the use of the electronic transducer is undesirably complex and relatively expensive. Additionally, the system can fail in several ways such as transducer failure, total detonation failure, or inoperably low detonation force. Moreover, this conventional detonation-based tubing pressure diversion system can be used only once--i.e., after an initial tubing pressure diversion to an external packer or other external pressure actuatable device the diversion apparatus cannot be used again in the well completion.
In view of the foregoing it can be readily seen that it would be highly desirable to provide improved tubing pressure diversion apparatus and associated methods which permit the internal tubing pressure to be elevated to a test pressure, prior to tubing pressure actuation of a packer or other external device, without the problems, limitations and disadvantages associated with conventional apparatus and methods such as those described above. It is accordingly an object of the present invention to provide such improved tubing pressure diversion apparatus and methods.